1. Field of the Invention
The present invention relates to heat-adhesive composite fibers which may be processed by heating into a nonwoven fabric or the like to provide a bulky product with a soft touch or feeling, and a method for making the same fibers.
2. Statement of the Prior Art
Many years have elaspsed since there were known in the art the side-by-side type or sheath-core type polypropylene base heat-adhesive composite fibers, which comprise two components having different melting points, and have a considerable portion, e.g., one half or more portion of their surfaces occupied by the component having a lower melting point. In the meantime, various improvements have been achieved. In the main, such improvements have aimed to improving the shrink properties of a web in processing the fibers into a nonwoven fabric by heating and enhance the strength, bulkiness and like factors of the resulting nonwoven fabric, and appreciable outcomes have been attained, but in terms of the bulkiness of the product the outcomes have not yet been satisfactory.
Hitherto, any appreciable outcome has not been attained in terms of not only the bulkiness but also the touch or feeling of nonwoven fabrics obtained from the polypropylene base heat-adhesive composite fibers by heating. Improvements in touch or feeling have been attempted as by using fine deniers or increasing the proportion of other fibers to be mixed with the composite fibers, such as rayon or wool, but have not still resulted in any product excelling in softness and bulkiness. The sitiuation being like this, a strong demand for further improvements in the bulkiness and softness of nonwoven fabrics intended for purposes such as paper diapers or sanitary materials is not satisfied. Thus, it is strongly desired to meet such a demand.